If electroconvulsive shock is given immediately after a learning session, retroactive amnesia for that response occurs. Such results may be due to production of aversive responses or to interference with consolidation of the neural engram, or to both. Aversive responses or competing responses are not adequate explanations for retroactive amnesia. Consolidation theory provides the most plausible explanation. The single-shock method is an appropriate approach for studying the relationships between electroconvulsive shock and retroactive amnesia.